In recent years, the widespread use of PCs and the Internet makes it possible to copy or edit digital content such as software easily. This being so, tamper-resistant techniques are needed to protect software against unauthorized alteration and analysis.
Research has long been performed on tamper-resistant techniques. For example, an article “Protecting Software against Inverse Analysis and Falsification” in Nikkei Electronics, Jan. 5, 1998, pp. 209-220 describes basic principles and concrete methods for preventing unauthorized software analysis. Also, an article “Software Tamper-resistant Techniques” in Fuji Xerox Technical Report, No. 13, pp. 20-28 deals with technical problems and measures concerning prevention of unauthorized software analysis.
Despite this research, more various techniques for protecting programs against malicious users are still needed.